LED-based lamps typically include a power converter (such as a transformer and/or rectifier) to convert an input AC mains voltage to a smaller DC voltage, driver circuitry to generate a constant current given the DC voltage, and LEDs that emit light when driven by the constant current. The driver circuitry may dim the LED by periodically and repeatedly “chopping” portions of the drive current down to zero amps; the nonzero portions of the drive current, however, remain at the constant level, effectively driving the LED with a series of constant-amplitude current pulses. By driving the LED with only one nonzero current value, the driver ensures the light output by the LED does not vary in color temperature.
Information may be encoded in the light output by the LED and transmitted therefrom in a similar fashion. The frequency or width of the constant-amplitude current pulses may be varied such that the changes in frequency and/or pulse width represent encoded information. One such technique, known as pulse-width modulation (“PWM”), samples an input data signal and represents its magnitude as a percentage of pulse width; maximum amplitude corresponds to 100% width, for example, while half amplitude corresponds to 50% width.
There are drawbacks to PWM-based LED driver circuits, however. The rapid switching may consume unnecessary power, and the frequency of switching may cause interference with other electronics. A need therefore exists for an improved method and system for transmitting information via light emitted by LEDs.